The design of linear power amplifiers for mobile applications requires high gain and linearity at the same time. More often than not, however, the gain and linearity characteristics are in trade-off relationship. An enhancement of one characteristic is achievable only at the cost of the other. Thus, the limited design range of parameters often prohibits satisfactory power amplifier design for high output power and high linearity. Therefore, the extension of design parameter range can be beneficial to power amplifier designers.
FIG. 1 illustrates a conventional cascode power amplifier having a simple stack of two transistors 101, 102. Source degeneration 106 can be used to enhance linearity of the power amplifier. Source degeneration 106 is a widely used linearization technique by providing a negative feedback path, that is, when high current flows through the cascode transistors, a high voltage can be generated across the degeneration element 106, and the gate-source voltage of the common-source transistor 101 decreases reducing the current again. However, this technique often degrades the gain of the power amplifier as well. Since the gain of power amplifiers is an important specification, it is undesirable to have excessive feedback.